Javascript – GET http://localhost:3000/registro 404 (Not Found) can someone help me?

I’m trying to make a post request in frontend to make a user register, but I’m having an error "404 not found"

file server.js

const express = require('express');
const connectDB = require('./config/conn');

const app = express();

//conectando o banco de dados
connectDB();

//iniciando o middleware
app.use(express.json({extended: false}));

app.get('/', (req, res) => res.send('API rodando'));

//Definindo rotas
app.use('/api/users', require('./routes/api/users'));
app.use('/api/auth', require('./routes/api/users'));


const PORT = process.env.PORT || 3000;

app.listen(PORT, () => console.log(`Server iniciado na porta ${PORT}`))

file Registro.jsx

import React, { useState } from 'react';
import '../auth/Registro.css';
import { Link } from 'react-router-dom';
import axios from 'axios';


const Registro = () => {
    const [formData, setFormData] = useState({ 
        nome:'', 
        email:'', 
        senha: '',
        senha2: ''  
    });

    const { nome, email, senha, senha2 } = formData;
    const onChange = e => setFormData({ ...formData, [e.target.name]: e.target.value });

    const onSubmit = async e => {
      e.preventDefault();
      if(senha !== senha2){
        console.log('As senhas devem ser iguais');
      } else {
        const newUser = {
          nome,
          email,
          senha,
          senha2
        }

        try {
          const config = {
            headers: {
              'Content-Type': 'application/json'
            }
          }

          const body = JSON.stringify(newUser);

          const res = await axios.post('/api/users', body, config);

          console.log(res.data);

        } catch (error) {
          console.error(error.response.data);
          
        }
      }
    }
  return (
    <div className='section_registro'>
    <p> Página de registro! </p>

      <form className='form' onSubmit={e => onSubmit(e)}>
          <label> Insira seu nome completo </label>
          <input 
          type="text" 
          name="nome"
          value={nome}
          placeholder='nome'
          required
          onChange={e => onChange(e)} />

          <label> Insira seu email </label>
          <input 
          type="email"
          name="email"
          value={email}
          placeholder='email'
          required
          onChange={e => onChange(e)} />
        
          <label> Insira sua senha </label>
          <input 
          type="password" 
          name="senha"
          value={senha}
          placeholder='senha'
          required
          onChange={e => onChange(e)} />

          <label> Confira sua senha </label>
          <input 
          type="password" 
          name="senha2"
          value={senha2}
          placeholder='senha'
          required
          onChange={e => onChange(e)}
           />

           <input type='submit' value='Registro' className='btn btn-primário'/>
        
        </form>

        <p> Já tem uma conta? </p> <Link to="/login"> Login </Link> 
          
    </div>
  )
}

export default Registro

file users.js

const express = require('express');
const router = express.Router();
const bcrypt = require('bcryptjs');
const { check, validationResult } = require('express-validator');
const jwt = require('jsonwebtoken');
const config = require('config');
const User = require('../../models/User');

//@route POST api/users
//@desc Registro de user 
//@acess Public
router.post('/', [
    check('nome', 'Nome é obrigatório').notEmpty(),
    check('email', 'Insira um email válido').isEmail(),
    check('senha', "Senha é obrigatória").notEmpty(),

], async (req, res) => {
    const errors = validationResult(req);

    if(!errors.isEmpty()){
        return res.status(400).json({ errors: errors.array() });
    }

    const { nome, email, senha, tipo } = req.body;

    try {

        let user = await User.findOne({ email });

        if (user){
            res.status(400).json({ errors: [{ msg: 'Esse user já existe' }] });
        }

        user = new User({
            nome,
            email,
            senha,
            tipo
        });

        const salt = await bcrypt.genSalt(10);

        user.senha = await bcrypt.hash(senha, salt);

        await user.save();

        const payload = {
            user:{
                id:user.id
            }
        }

        jwt.sign(
            payload, 
            config.get('jwtSecret'), 
            { expiresIn: 36000 }, (err, token) => {
                if(err) throw err;
                res.json({ token });        
            });
        
    } catch (err) {
        console.error(err.message);
        res.status(500).send('Server error');     
    }
    }
);

module.exports = router;

idk why the browser is showing this error. It’s seems like my frontend is not "finding" my backend.
error: GET http://localhost:3000/registro 404 (Not Found)

I tried change the folder of backend and the path in server.js, but it didn’t work. after that, I’m having the error that I can’t get the register router, but I had the error POST http://localhost:5000/api/users 404 (Not Found)

What I am doing wrong?